The TooManyListenersException Exception is used as part of
the Java Event model to annotate and implement a unicast special case of
a multicast Event Source.

The presence of a "throws TooManyListenersException" clause on any given
concrete implementation of the normally multicast "void addXyzEventListener"
event listener registration pattern is used to annotate that interface as
implementing a unicast Listener special case, that is, that one and only
one Listener may be registered on the particular event listener source
concurrently.